Various printing techniques have been developed over time to increase the speed and reduce the cost of printing an item. However, more recently, individualized printed products or individualized sets of product have become desirable, such as, for example, individualized cards such as credit cards, gift cards, loyalty cards, membership cards, identification cards or tags, point of sale activated cards, telephone cards, etc. These types of products have required individual codes, characters or other depictions printed on individual items. Requirements for individualization have resulted in a variety of constraints affecting parameters such as printing quality, speed, cost, durability, resolution and materials.
A number of printing techniques have been used to print individualized items or sets of items, such as card substrates or other objects. One of such techniques is thermal transfer printing. Thermal transfer printing typically consists of printing from a colored ribbon, e.g. a pigmented foil resin ribbon, and transferring a dye or pigmented resin onto a card. In many instances in order to get good pigment adhesion to the substrate, thermal transfer printing includes melting the resin into the surface of the substrate, typically a plastic such as polyvinylchloride (PVC). One problem with thermal transfer printing techniques is that the quality of the printing may be compromised by debris on the item. In addition, this debris can damage the print heads used and cause costly repairs. Unprinted areas or gaps in printing may be formed, e.g., by damaged printheads or a wrinkled ribbon, and thus the consistency of appearance quality may be compromised. In addition, the printed image has poor durability; it can be removed through the use of a common, ordinary pencil eraser.
Other printing techniques used for such individualized items or sets include embossing of characters, dye sublimation to form characters and laser techniques to etch, heat or burn printing into the surface or core of an item. Some of these techniques have been relatively slow and inefficient, requiring costly materials and equipment. These techniques typically require special substrates, safety shielding and ventilation. Still other of these printing techniques such as xerography, require special substrate materials to accept the toner from the drum and are not designed for individuated items but rather for sheets of materials.
Some faster, more efficient technologies, such as ink jet printing have been used in printing individual items. In general, current ink jet printing techniques involve directing droplets of inks through the air onto a substrate. Currently two different types of inkjet printing are being commercially utilized: continuous and drop on demand ink jet printing. Continuous ink jet printing provides a continuous flow of ink through or within the printhead during the process. Continuous ink jet printing typically involves chargeable organic solvent or water based inks that are directed onto a surface by providing a continuous stream of droplets of ink that are either charged or not charged according to a desired printed image or template. In some systems, the un-charged drops are printed onto to the substrate while the charged drops are deflected and not printed. Conversely, in other systems, the charged droplets print. Other continuous ink jet systems use a variable deflection voltage to steer the individual droplets. Because the continuous ink jet process requires a continuous stream of ink be supplied, the inks selected typically have a low viscosity. Also, the selected inks typically become integrated with the surface on which they are printed because the typically selected solvents (e.g., acetone and methylethylketone) permit this.
One disadvantage of continuous ink jet products is that the resolution and durability are not high. Another disadvantage is that the flight of the droplets is not always consistent resulting in a poor image appearance, e.g., wavy bars in bar codes and text. This may affect the desired appearance and/or the readability of the coded information in certain applications. Furthermore, continuous ink jet printing is not economical requiring continuous flow of ink through or into the printhead and thus more ink and fluid. Continuous ink jet printing also has highly complex equipment with high maintenance costs. Continuous ink jet printing processes have been used to print on insulated wires where the insulated wires come in a long continuous strands. The insulation of the wires has been plasma treated to improve adhesion of the ink to the substrate. This process uses organic solvent-based inks that become integrated with the surface of the insulation on which they are printed and the process is not used to control flow of droplets over the surface after being applied.
Non-continuous ink jet printing uses solvent or water-based inks and apply ink on demand (“drop on demand” application or “DOD”). This type of printing technique is used in lieu of continuous ink jet printing to print items. The advantages of using DOD ink jet printing are that there are lower consumable costs such as ink and other fluid, lower capital costs and lower maintenance costs. However, one disadvantage to this technique is that because the ink in a printhead is not continuously used, it may dry on face of the printhead leading to poor print quality. Accordingly, slower drying solvents are used and thus the inks commonly used in drop on demand printing techniques do not dry quickly when applied to a substrate surface. The slower dry time increases the chances that the ink droplets will spread in an undesirable or uncontrolled manner across the substrate. The individual droplets of ink will fail to spread sufficiently or will spread too much. This is particularly the case with items made of non-absorbent or less absorbent substrates such as plastics. It is believed that dry time in drop on demand printing processes tends to affect appearance negatively at least in part because drop on demand inks are typically less volatile, e.g., than continuous ink jet printing ink, and in using less volatile inks, the dry time tends to allow the printed ink to flow for a longer duration on the substrate, which will alter appearance. Also, inks used in drop on demand printing tend to sit on the top of the substrate more while continuous ink jet inks attack and penetrate the substrate. Thus continuous ink jet inks will tend to integrate more with the substrate surface.
Accordingly, appearance of the printed image using drop on demand printing may be negatively affected. Additionally, the results of image quality using drop on demand printing can be unpredictable, particularly with relatively less absorbent substrates such as the PVC or other plastic cards that are typically used for individually coded transaction cards. The substrate materials and printing surface conditions tend to vary widely from type, form, material, condition, and age of the substrate, and from batch to batch, from piece to piece of substrate of the same or similar construction and at various locations on the surface of a particular substrate. Thus the results of printed image quality have varied in different locations on individual items, from item to item and batch to batch. Attempts have been made to treat the substrates with coatings or primers to reduce surface variability. However, they are typically applied to the substrate and dried or cured in a separate step, which introduces additional manufacturing steps and costs. They also change the consistency of appearance of the substrate. Coatings and primers change the glossy appearance from a continuous uninterrupted sheet to a patchwork like configuration of different surfaces. Some coatings have covered the desired glossy surface of the card. Because of their receptivity to inks, coatings and primers tend to attract dirt markings and will lead to a poor appearance over time.
Furthermore, the appearance and image quality of the product may be compromised over time and usage of the product. The appearance, edge contrast and/or color density of a printed image may be of particular importance in certain applications such as bar codes and products where such parameters have performance or marketing significance. Images printed with non-continuous ink jet printing (and other printing processes) can be easily rubbed off in normal use. In certain products, the printed images may subjected to conditions where the printed image is rubbed or used under physical conditions that cause the image appearance, edge contrast and color density to degrade over time. For example, transaction cards are subjected to repeated rubbing when read by a scanner or other conditions where the user carries, uses and stores the card. It would therefore be desirable to provide a printed image having improved durability over time and usage of the product.
All these printing techniques have had other problems including, slow dry time, poor resolution, and poor durability. Some printing systems such as ink jet systems, thermal transfer printing and dye sublimation have had such poor durability that they require an additional coating or clear layer on top of the printing to protect the printed image.
Furthermore, printing individuated items consistently has had various challenges and problems. Variations occur on the surface from item to item and in different areas on the same item. Other surface effects may occur from, e.g., handling when printing, finger prints, scratching when feeding or rubbing, and other non-visible surface effects that occur when the individual items are handled or fed onto a conveyor.
Accordingly it would be desirable to provide improved individualized and/or individuated printed products with greater durability, resolution, appearance, and consistency of image quality that may be efficiently produced.
It would also be desirable to provide individualized transaction cards, such as cards with codes or identification printed thereon, with greater durability and resolution.
It would also be desirable to provide an improved drop on demand printer and printing method that improves the appearance and consistency of product image quality of items printed with a drop on demand printer.